Polycrystalline diamond (PCD) is a super-hard, also known as superabrasive material comprising a mass of inter-grown diamond grains and interstices between the diamond grains. PCD may be made by subjecting an aggregated mass of diamond grains to an ultra-high pressure and temperature. A material wholly or partly filling the interstices may be referred to as filler material. PCD may be formed in the presence of a sintering aid such as cobalt, which is capable of promoting the inter-growth of diamond grains. The sintering aid may be referred to as a solvent/catalyst material for diamond, owing to its function of dissolving diamond to some extent and catalyst its re-precipitation. A solvent/catalyst for diamond is understood be a material that is capable of promoting the growth of diamond or the direct diamond-to-diamond inter-growth between diamond grains at a pressure and temperature condition at which diamond is thermodynamically stable. Consequently the interstices within the sintered PCD product may be wholly or partially filled with residual solvent/catalyst material. PCD may be formed on a cobalt-cemented tungsten carbide substrate, which may provide a source of cobalt solvent/catalyst for the PCD.
PCD may be used in a wide variety of tools for cutting, machining, drilling or degrading hard or abrasive materials such as rock, metal, ceramics, composites and wood-containing materials. For example, PCD elements may be used as cutting elements on drill bits used for boring into the earth in the oil and gas drilling industry. In many of these applications the temperature of the PCD material may become elevated as it engages a rock formation, workpiece or body with high energy. Unfortunately, mechanical properties of PCD such as hardness and strength tend to deteriorate at high temperatures, largely as a result of residual solvent/catalyst material dispersed within it.
U.S. Pat. No. 3,745,623 discloses a PCD element comprising a polycrystalline diamond layer bonded to a cemented carbide body comprising 94 weight percent tungsten carbide and 6 weight percent cobalt. U.S. Pat. No. 4,380,471 discloses the various grades of cemented tungsten carbide may be used as substrates for PCD elements, including the following grades from the Carboloy® range: 44A, 90, 883 and 999, which comprise 6, 10, 6 and 3 weight percent cobalt, respectively. U.S. Pat. No. 5,304,342 discusses that for a given application, it is desirable to provide the stiffest possible WC—Co cemented carbide substrate, thereby minimizing the deflection of the PCD layers and reducing the likelihood of PCD failure. However, if the modulus of elasticity is too high, the inserts are prone to break off during drilling.
U.S. Pat. No. 5,667,028 discusses that as a bit rotates, the edge of the PDC cutting layer of a PCD cutter makes contact and “cuts” away at a formation being drilled. At the same time portions of the exposed cutter body also make contact with the formation surface. This contact erodes the cutter body. It discloses an improved polycrystalline diamond composite (“PDC”) drag bit cutter comprising multiple cutting surfaces, at least two of which are non-abutting, resulting in an enhanced useful life. Fluid erosion of the PDC cutter may also occur.
U.S. Pat. No. 5,431,239 discloses a composite stud structure having different material characteristics across its structural cross section to provide the abrasion resistance of hard materials combined with fracture resistance, called fracture toughness. In one embodiment a stud is comprised of an inner core of material having higher or enhanced fracture toughness, such as large-grain-size tungsten carbide or high-cobalt-content tungsten carbide, surrounded by an outer layer of hard, abrasion resistant material. A typical material is low-cobalt, cemented tungsten carbide. Although 6% cobalt is possible, about 9-12% cobalt is the range preferred. Cobalt content usually ranges between 6 and 20 percent in cemented tungsten carbides. High cobalt content is greater than about 15%. Carbide grain size and cobalt content can both be varied to design for strength or high fracture toughness. The cutting face is usually manufactured of a superhard material such as polycrystalline diamond.
U.S. Pat. No. 6,216,805 discloses a cutting element that includes a base including an erosion-resistant and abrasion-resistant material. A cutting end of the cutting element is configured to have a superabrasive cutting table secured thereto. In an embodiment, the base is fabricated from an erosion-resistant and abrasion-resistant material. For example, the base may comprise carbide (e.g., tungsten carbide) and a binder material (e.g., cobalt). When relatively more binder is employed to fabricate base, the erosion-resistance and abrasion-resistance of base decrease. Cemented carbide structures that have smaller grains of carbide are also typically more erosion-resistant and abrasion-resistant, but less tough, ductile, and impact-resistant, than cemented carbide structures formed with larger grains of carbide.
U.S. Pat. No. 6,258,139 discloses a PDC (polycrystalline diamond compact) with an internal diamond core in the substrate, to provide additional diamond for exposure when the substrate is sufficiently eroded. Also disclosed is a PDC with an internal carbide core, which is entirely enclosed by the diamond region of the PDC cutter, to avoid high tensile stresses in the diamond region.
Freinkel discloses that WC grain size in the range from 1.6 microns to 2.2 microns results in optimum erosion resistance for cemented WC (“Energy loss mechanisms in the erosion of cemented WC”, Scripta Metallurgica, 23, 1989, pp. 659-664).
U.S. Pat. No. 7,017,677 discusses that existing substrates for shear cutters are generally formed of cemented tungsten carbide particles with grain sizes in the range of about 1 to 3 microns and cobalt content in the range of about 9 percent to 16 percent by weight, and have hardness in the range of about 86 Ra to 89 Ra.
U.S. Pat. No. 7,556,668 discloses an embodiment of a consolidated hard material made from approximately 75 weight percent hard particles, such as WC, and approximately 25 weight percent binder material, such as Co. Also disclosed are polycrystalline diamond compact (PDC) shear-type cutters wherein hard materials disclosed in the patent may be used to form a shear cutter substrate that is used to carry a layer or “table” of polycrystalline diamond that is formed on it at ultrahigh temperatures and pressures.
There is a need for polycrystalline diamond compact (PDC) cutter elements having improved overall erosion resistance without substantially compromising fracture resistance.